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Fatemeh Tabatabaei
Instituto de Astrofisica de Canarias
Collaborators:
A. Basu, R. Paladino,
D. D. Mulcahy, J. Beckman, J.H. Knapen
Cloud-Scale GMRT Survey of M33: Unveiling the Low-Frequency Properties
of the ISM
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RC an extinction-free SFR tracer
SED of an idealized HII
Mid-radio continuum (MRC: 1-10GHz) the most precise measure of SFR
How precise is to measure SFR at
lower frequencies?
Tabatabaei et al. 2017
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Radio Spectrum of an idealized HII region
Ideal tracer of old cosmic ray electrons (CREs):
star formation history galaxy evolution
What if the ISM condition differs from that in the MW?
Giant HII regions?
ISM studies mostly in the MW(e.g. Kassim 1990, Brogan 2003)
Low Frequency RC Ideal Tracer of SF History
Tomography of CR emissivity using opaque HII regions (Kassim 1990)
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NGC604
IC142
NGC595
B690
B61/62
NGC548
IC131
NGC592
B691
IC133
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Synchrotron emission is extended, yet strong near SF regions
enhanced magnetic field/fresh CREs?
TRT Separation Technique: Synchrotron spectral index varies in the disk
as CREs experience various energy losses (Tabatabaei et al. 2007& 2013a)
Mid-Radio: GHz Thermal & Nonthermal Emission @ 200-pc resolution
Thermal Nonthermal
B690 B690 N604 N604
N595 N595
N592 N592
N548
B61/62 B61/62 IC141IC141 IC131
IC133
IC132
B691 B691
IC132
IC131
IC133
N548
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Amplification of Magnetic Fields in SF Regions
0.050.20SFR B
B - SFR correlation agrees with
supernova-driven dynamo models (Gressel+2000)
Global studies: Chyzy+2008,09, Heesen+2014,
FT+2017
Magnetic Field (color) & SNRs (+) µG
Tabatabaei et al. 2013
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• α_n=1.0 ±0.1 in between the arms and the outer parts Inverse Compton +synchrotron energy loss
• α_n≈0.5 in star forming regions: injection of CREs
• Even flatter in giant HII regionsdifferent acceleration regimes?
High-resolution surveys
Injection of Cosmic Rays in SF Regions
Tabatabaei+2007
0.5 1.0
N604
IC131
IC133
N595
IC132
N548
B691
B690
N592
n
S
n
90‘‘~ 360 pc
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Cloud-Scale Surveys of SF & ISM in M33 (≥ 40pc resolution)
~ same res. as HerM33es and CO/HI observations
The JVLA Surveys:
L-band (12 point.), C-band (25 point.)
The GMRT 320 MHz Survey
(4 ponit.)
~20 arcmin
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The JVLA Observations (6.3 GHz)
N604
IC131
N595
N592
B61/62IC141
B690
B691
resolution= 10’’ ~ 40pcrms=7 µJ/beam
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The GMRT Observations
45 facets for each 4 point. ~3° x3° around M33
Natural weighting (Robust=5)rms=0.35 mJy/beam
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M33 at 320 MHz: 25”~ 100pc resolution
Contours: JVLA 6GHzColor: GMRT 320 MHz
Galaxy Structures:
- The Galaxy center
- Inner 3kpc bright
- The spiral arms NI, SI, SII
- Segments of other arms
- SF regions?
NI
SII
SV
SIII
SI
NIV
NV
Robust=5, rms=0.35 mJy/beam
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Absorption in Some Regions
α= -0.37
α= -0.67
α=-0.22
α= 0.07
α= -0.30
α= -0.06
SEDs of the HII regions
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…And Globally?
Contours: Nonthermal 1.4 GHz(separated using TRT method, Tabatabaei+ 2013)
BG
BG
BG
BG
BG
General trend:
Bright 320MHz emission where the GHz nonthermal
emission is bright
The radio spectrum of giant HII:
Steeper at ʋ<1 GHz, as the thermal emission is absorbed indicative of pure SNRs, or the nonthermal ISM (enhanced B due to SF feedback)
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Radio - IR Correlation
320 MHz RC: better correlated with 160µm than with 24µm
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Summary
• Giant HII regions/SF complexes show up as bright sources at low-frequncies mostly due to their nonthermal emission as first indicated at GHz using the TRT separation in M33.
• The 320MHz and CO correlated but weaker than GHz-CO correlation possibly due to free-free absorption in a cold ionized gas.
• The 320MHz-IR correlation is better with colder dust traced by 160µm than with warmer dust.
• The absorption effects should be taken into account measuring SFR at low-frequencies.
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Amplification of the magnetic field in SF regions
Ordered Magnetic Field
Tabatabaei+2008
The total B strength and SFR correlated
0.050.20SFR B Ordered field depends on large-scale dynamics, galaxy rotation:
Fletcher+2011, Tabatabaei+2016
Agrees with Supernova-driven dynamo models (Gressel+2000, see also Chyzy+2008,09, Heesen+2014)